A conventionally used cold rolling oil includes a substance such as a mineral oil, animal and vegetable fat and oil, and synthetic ester, or a mixture thereof, as a base oil, into which an oiliness improving agent such as a fatty acid; an extreme-pressure additive such as a phosphoric ester; an anti-rust additive; an antioxidant; an emulsifier, and the like are blended. Usually, this cold rolling oil is emulsified and dispersed in water to be used as an emulsive dispersion having a concentration of approximately from 1 to 10% by volume.
This emulsive dispersion is generally called a coolant; and is usually used in a circulation method, by which the emulsive dispersion is sprayed at a work roll and a steel sheet from a nozzle by way of a pump from a tank, and returned to the tank. The cold rolling oil used in this circulation method exerts a lubricating effect by function of being spread and deposited over the work roll and the surface of the steel sheet (the function being called a plating-out property).
In recent years, with the advance in rolling technologies, high rolling speed and mass production have been attempted; and it is desired to further improve a lubricity, and an emulsion stability at a time of circulation, of a metal rolling oil. Patent Documents 1 to 3 disclose metal rolling oil compositions which exhibit excellent emulsion stabilities and plating-out properties.    Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 08-325588    Patent Document 2: JP-A No. 10-298580    Patent Document 3: JP-A No. 2008-007544